The odd one out in this list is option 'D' UNESCO.

Explanation:
- The given options are all international organizations, but UNESCO stands out as it has a different focus compared to the others.
- The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. It focuses on coordinating and providing guidance on health-related issues globally.
- The World Trade Organization (WTO) is an intergovernmental organization that deals with the global rules of trade between nations. Its main objective is to ensure the smooth flow of trade and promote fair competition.
- The International Labour Organization (ILO) is a United Nations agency that focuses on promoting social justice and internationally recognized labor rights. It sets labor standards, develops policies, and provides technical assistance to member countries.
- The United Nations Conference on Trade and Development (UNCTAD) is a permanent intergovernmental body that deals with trade, investment, and development issues. Its main goal is to help developing countries integrate into the global economy and benefit from international trade.
- On the other hand, the United Nations Educational, Scientific and Cultural Organization (UNESCO) is primarily focused on promoting international collaboration in the fields of education, science, culture, and communication. It aims to protect cultural heritage, foster freedom of expression, and promote educational development.

In summary, while WHO, WTO, ILO, and UNCTAD are all international organizations that primarily focus on public health, trade, labor rights, and trade and development respectively, UNESCO stands out as it has a distinct focus on education, science, culture, and communication. Therefore, the odd one out is option 'D' UNESCO.